1. Field of the Invention
This invention relates in general to processes for treating waste water skimmings. In particular, the invention relates to processes for separating streams comprising water, oily material, and solids in varying percentages, into: a dry solid product containing low percentages of fats, oils and greases; a dry, solids-free oily product; and an oil-free, solids-free water stream.
2. Description of the Related Art
Waste water skimmings from food processing plants generally consist of mixtures and emulsions of a continuous water phase and a discontinuous oil phase, with varying percentages of entrained solids. These mixtures tend to be difficult to separate by conventional means. Also, the solids produced by most of the available processes have relatively high percentages of oily material and are often unsuitable for commercial purposes and must be discarded.
Conventional methods for processing these types of streams use evaporation, centrifuging and other energy intensive processes for separating the water and oily material. For example, U.S. Pat. No. 4,728,428, issued to Broussard, Sr., on Mar. 1, 1988, discloses a method utilizing a wet spiral absorber/contactor. The mixture of solvent and oily water is then separated in a settling tank. This method does not address treatment of liquid streams containing any substantial amount of solids.
U.S. Pat. No. 5,186,817, issued to Pakpek et al., on Feb. 16, 1993, discloses a process for treating mixtures of petroleum compounds and water by inverting the oil/water emulsion using high shear mixing. The process requires analysis of the mixture to ensure that the emulsion is inverted. The process also uses pressurized vessels and other equipment that raise its construction costs.
A need remained for a waste treatment process capable of inexpensively separating the oily material and solid components from waste water skimmings and turning them into higher value products. A process requiring less energy consumption for each pound of material processed was also desired. In addition, a process that requires inexpensive, commonly available equipment was desired. A process that operates predominantly at about atmospheric pressure and temperatures common in food processing plants (below 225 degrees Fahrenheit [107 degrees Celsius]) was also desired.